Mesenchymal chondrosarcoma of the retroperitoneum. Report of a case diagnosed by fine needle aspiration biopsy with immunohistochemical, electron microscopic demonstration of S-100 protein in undifferentiated cells.

BACKGROUND: Mesenchymal chondrosarcoma (MC), first described in 1959 by Lichtenstein and Bernstein, is an uncommon tumor of the soft tissues and bone defined by the coexistence of nests of well-defined cartilaginous tissue within a proliferation of primitive mesenchymal cells. CASE: A 27-year-old, white female consulted a physician for a left lumbar mass associated with sciatica-type pain, asthenia, anorexia and weight loss. Abdominal computed tomography showed a 20-cm, retroperitoneal neoplasm that occupied the lower half of the left abdominal flank. Fine needle aspiration biopsy showed clusters of small round cells mixed with islets of mature cartilage. Immunomarking for electron microscopy, carried out with 15 nm of A protein/colloidal gold, showed specific immunoreactivity to S-100 protein in the nuclear chromatin, nucleoli, Golgi apparatus, plasma membrane and cytosol of cells with more developed organelles.
CONCLUSION: The diagnosis of MC rests on recognition of the biphasic component of small, undifferentiated cells and cartilage islets. In aspirates with only undifferentiated cells, demonstration of ultrastructure-specific immunoreactivity to S-100 protein may contribute to the final diagnosis.